An In Vivo Study to Determine a Mathematical Formula to Relate Horizontal Condylar Guidance Angle Derived Clinically and Radiographically

INTRODUCTION

The major goal of prosthetic rehabilitation is restoring the esthetics and functional efficiency of the patient.¹ Whatever may be the treatment that the prosthodontist plans, it should be in harmony with the patient’s stomatognathic system. Nature has blessed us with a marvelously dynamic stomatognathic system, which allows us to function and therefore exist.²

One major factor that contributes to its functional efficiency is the occlusion. Occlusion is the static relationship of the teeth and is fundamental to all aspects of dentistry.^1,2 Occlusion is influenced by factors like anterior and posterior determinants.² Condylar guidance is the posterior determinant of occlusion and this concept is well established in dentistry. Although incisal guidance and cuspal angle are gaining importance as determinants of occlusion,³ condylar guidance cannot be overlooked. Thus, in completely edentulous patients, while attempting to restore the lost occlusion, the importance of condylar guidance should be considered. Condylar guidance is the mandibular guidance generated by the condyle and articular disk traversing the glenoid fossa (GPT-8). It is considered to be a stable factor because it is unalterable in healthy patients.⁴ However, in the case of trauma, pathology, it alters.

In clinical dentistry, it appears to be a common belief that mandibular movements in vivo can be reproduced to a large extent with the use of adjustable articulator,⁵ but one factor governing these movements of the adjustable articulator is the sagittal condylar guidance angle (SCGA). The methods used to determine the inclination of the sagittal path of condyles are:⁶

One method is based on the Christensen phenomenon, which consists of employing intraoral protrusive records and then calculating the angle in the articulator by programming (Posselt). A graphic method in which the condylar path is recorded on a card by means of a face bow (Gysi technique, McCollum technique) and a radiographic techniques (Panoramic radiographs, Cineradiographs).

Direct interocclusal records are most commonly used because of their simplicity according to Dawson. But many authors have stated that errors can occur because of the technique used in recording and transferring the records from dental arches to an articulator.⁷ By using the graphic method, there is less influence of possible errors⁶ from poorly adapted recording bases. But fixation of the tracing plates or papers during tracing is a probable source of error in this method.

Although radiographic methods like cineradiography and panoramic radiography cause radiation exposure to the patient, they were found to be useful in setting the condylar guidance angle.^8–10 However, effective may be the techniques existing, each has its own merits and demerits. A combination of two or more techniques helps in decreasing errors. So, the present in vivo study relates the sagittal condylar guidance angle derived clinically using interocclusal records and radiographically using panoramic radiographs using a mathematical equation since mathematical equations are highly effective in comparing biological values.

MATERIALS AND METHODS

RESULTS

The angle formed by the intersection of the two planes (FH plane and mean condylar path) gives the sagittal condylar guidance angle. This was obtained on both sides and tabulated (Tables 1, 2, and Figs 5 to 7).

The model of regression for right side was hypothesized and equation obtained was y = −0.080x + 23.49, while the model of regression for left side was hypothesized and equation obtained was y = −0.101x + 25.12, where y = dependent variable (condylar guidance value obtained by panoramic radiographs) and x = constant variable (condylar guidance value obtained by protrusive interocclusal records). The present study found that on the right side, there was a statistically significant (p = 0.019) difference in the mean protrusive interocclusal records (17.04 ± 6.61) and the panoramic radiographs (22.12 ± 7.2) whereas it was not significant (p = 0.101) on the left side.

DISCUSSION

If the philosophy of balanced occlusion is accepted as the desirable and professional method of using denture teeth, the condylar path should be determined on the patient and set on the articulator so that the patient’s TMJ is in harmony with the occlusion as programmed on the articulator.

Recording the condylar guidance angle is a prerequisite for any prosthetic rehabilitation, though it is a clinical challenge. The sagittal condylar path as measured in a living body has a convex S-shaped curvature inferiorly.³ According to Aull,¹³ the sagittal condylar path showed a straight line in only 8% population, and in the remaining 92%, it was a curved path.

Currently, the method in use for recording condylar guidance is a combination of graphic and interocclusal record methods. For the making of interocclusal records, different authors suggested different materials like irreversible hydrocolloids, zinc-oxide eugenol paste, elastomeric materials, interocclusal waxes, each having its merits and demerits. The reliability of these materials has been questioned in different studies^7,8,14 This has led to the search for new methods for obtaining SCGA, like the radiographs.^9,10,15–21

However, the limitations of the radiographic method are panoramic distortion, head and reference plane orientation,²⁰ and difficulty in distinguishing the articular eminence outline from the zygomatic arch. The positions of the two reference lines relative to each other may vary if there is a change in beam direction due to positioning errors.

In the present study, the SCGA values obtained from both methods are tabulated (Table 1) and statistically analyzed. Data analysis showed that the protrusive interocclusal records on the right side were 17.04 ± 6.61 (mean ± S.D), whereas it was 19.18 ± 8.12 on the left side. Similarly, panoramic radiographic records of the patients were analyzed; data revealed that the panoramic radiographs angle on the right side was 22.12 ± 7.20 and on the left side it was 23.17 ± 7.66 (Table 2). The present study found that on the right side, there was a statistically significant (p = 0.019) difference in the mean protrusive interocclusal records (17.04 ± 6.61) and the panoramic radiographs (22.12 ± 7.2) whereas it was not significant (p = 0.101) on the left side (Table 1 and Figs 6 and 7).

Pearson correlation was done to obtain a correlation between protrusive interocclusal record and panoramic radiographs on the right and left sides. On the right side, the r value was −0.074 and the p value was 0.745 which indicates condylar guidance angles obtained by protrusive interocclusal records and panoramic radiographs are negatively correlated. On the left side, r value was −0.108 and the p value was 0.633 which indicates condylar guidance angles obtained by the protrusive interocclusal record and panoramic radiographs are negatively correlated. A simple linear regression analysis was done on the right and left sides which showed that there is a negative best fit line on both sides. The condylar guidance value obtained by the panoramic radiograph increases when the values obtained by protrusive interocclusal records decreases.

The model of regression (obtained by statistical analysis) for the right side was hypothesized and the equation obtained was y = −0.080x + 23.49, where y = dependent variable (condylar guidance value obtained by panoramic radiographs) and x = constant variable (condylar guidance value obtained by protrusive interocclusal records). The correlation coefficient was −0.074 on the right side (negative correlation) (Fig. 6).

The model of regression for the left side was hypothesized and the equation obtained was y = −0.101x + 25.12, where y = dependent variable (condylar guidance value obtained by panoramic radiographs) and x = constant variable (condylar guidance value obtained by protrusive interocclusal records). The correlation coefficient was −0.108 on the left side (negative correlation).

The present study results were in line with Zamacona et al.,⁶ which stated condylar path inclination is variable on the left and right sides. A study by Gilboa et al.,⁹ stated panoramic radiographs replicated the articular eminence in dry human skulls with a mean difference of 7° which was similar to the present study.

Similarly, the present study is comparable with Shah et al.,¹⁷ who observed that condylar guidance values by the radiographic method were >1.97° and 3.18° than the protrusive interocclusal method from the right and left sides, respectively. Also coinciding with the present study were results obtained in studies by Shah et al,¹⁹ Venkateshwaran et al.²⁰

However, results were contrary to the results obtained by Patil et al.²¹ who stated that condylar guidance values did not differ between Hanau H2 and OPG.

Limitations of the present study were the number of subjects which were 22, and there lies a confliction on the stage at which the radiograph should be taken. There was a statistically significant difference between the condylar guidance values obtained during jaw relations, wax try-in, denture insertion, and the radiographs taken at all those stages.¹⁰ The present study did not consider this factor and has taken the angle obtained during the try-in stage as it was proved to be nearer to the radiographic angle. Thus, we suggest further studies to be conducted with increased sample size and taking into consideration the stage at which the radiograph is taken.

CONCLUSION

From the observations, it can be concluded that the radiographically obtained condylar guidance angles were higher than the clinically derived angles. There was a significant correlation between both the angles on the right side rather than on the left side. The probable reasons for the difference between both sides could be the change in the anatomy of the TMJ and also due to variation in direction and magnitude of condylar movements. In cases where taking the clinical records is not possible, radiographs can be taken as an aid in assessing the condylar guidance angle, rather than relying on the average values.

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